Peisheng Mao

Effects of adult neighbour and gap size on seedling emergence and early growth of Bromus inermis Leyss

A field study was conducted to determine the effects of neighbour root exclusion and gap size on the seedling emergence and early growth of Bromus inermis. Seeds of B. inermis were added to artificially created gaps in an improved shortgrass steppe in northern China. Neighbour root exclusion was accomplished using PVC tubes sunk in the soil of gaps. Emergence and survival of seedlings were greater in all gaps than in the control (0-cm diameter), but better growth performance (height of seedling, leaves, tillers and dry weight per seedling) was observed only in large gaps (20- and 40-cm diameter) with neighbour root present and gaps without neighbour root presence. Seedling growth performance was improved by reducing root and shoot competition. Neighbour root exclusion provided a favourable environment for seedling establishment. Differences between gaps in light levels and topsoil temperature can explain the patterns of germination. These results confirm that B. inermis is a gap-enhanced species. Our study strongly suggests that asymmetric competition by adult neighbour plants negatively influences the establishment of B. inermis.

Contribution of the pod wall to seed grain filling in alfalfa

Three genotypes of alfalfa viz. Medicago sativa (Zhongmu No. 1, Zhongmu No. 2) and M. varia (Caoyuan No. 3) grown in the filed were investigated for the contribution of pod wall and leaves by shading all pods and leaves on July 15, 20 and 25, respectively. Date was recorded for total pod weight (TPW), pod wall weight (PWW), seed weight per pod (SWP), seed number per pod (SNP) and single seed weight (SSW) of one-coil and two-coil spiral pods. TPW, SNP, PWW and SWP were reduced by shading all leaves or pods, whereas SSW was not significantly affected. The relative photosynthetic contribution of pod wall to SWP was 25.6–48.1% in three genotypes on July 15. The pod wall in one-coil spiral pods generated a greater relative contribution to the TPW and SWP than in two-coil spiral pods. In the last stage (July 25), the relative photosynthetic contribution of leaves to SWP sharply decreased, whereas the relative photosynthetic contribution of pod wall to SWP was stable in the late stage (July 20 and 25). In conclusion, the pod wall of alfalfa could carry out photosynthesis and the pod wall played an important role in pod filling at the late growth stage.

Grazing effects on ecosystem CO2 fluxes differ among temperate steppe types in Eurasia.

Grassland ecosystems play a critical role in regulating CO2 fluxes into and out of the Earth’s surface. Whereas previous studies have often addressed single fluxes of CO2 separately, few have addressed the relation among and controls of multiple CO2 sub-fluxes simultaneously. In this study, we examined the relation among and controls of individual CO2 fluxes (i.e., GEP, NEP, SR, ER, CR) in three contrasting temperate steppes of north China, as affected by livestock grazing. Our findings show that climatic controls of the seasonal patterns in CO2 fluxes were both individual flux- and steppe type-specific, with significant grazing impacts observed for canopy respiration only. In contrast, climatic controls of the annual patterns were only individual flux-specific, with minor grazing impacts on the individual fluxes. Grazing significantly reduced the mean annual soil respiration rate in the typical and desert steppes, but significantly enhanced both soil and canopy respiration in the meadow steppe. Our study suggests that a reassessment of the role of livestock grazing in regulating GHG exchanges is imperative in future studies.

Assessing of the contributions of pod photosynthesis to carbon acquisition of seed in alfalfa ( Medicago sativa L.)

The distribution of carbon from a branch setting pod in alfalfa was investigated during the seed development of seeds to determine the relative contribution of pod and leaf photoassimilates to the total C balance and to investigate the partitioning of these photoassimilates to other plant organs. A 13Clabeling procedure was used to label C photoassimilates of pods and leaves in alfalfa, and the Δ13C values of a pod, leaves, a section of stem and roots were measured during seed development on day 10, 15, 20 and 25 after labeling of the pod. The results showed that the alfalfa pod had photosynthetic capacity early in the development of seeds, and that pod photosynthesis could provide carbon to alfalfa organs including seeds, pods, leaves, stems and roots, in addition to leaf photosynthesis. Photosynthesis in the pod affected the total C balance of the alfalfa branch with the redistribution of a portion of pod assimilates to other plant organs. The assimilated 13C of the pod was used for the growth requirements of plant seeds and pods. The requirements for assimilated C came primarily from the young pod in early seed development, with later requirements provided primarily from the leaf.

Smooth bromegrass seed yield and yield component responses to seeding rates and row spacings in two climates

Abstract Successful grass seed production depends on identifying a suitable environment for the species and proper agronomic practices. Previous research on many species has addressed identifying appropriate agronomic practices for grass seed production, but these studies have not evaluated the effects of environment. By conducting the same experiments in Jiuquan, China (a desert climate) and Tongliao, China (a semiarid continental monsoon climate), the effects of environment, seeding rate, row spacing and their interactions were determined for smooth bromegrass (Bromus inermis Leyss) seed production. Three seeding rates (.3, .5, and .7 g m−1 pure live seed) and four row spacings (30, 50, 70, and 90 cm) were evaluated over three years. Jiuquan had comparable seed yield (SY) and greater thousand-seed weight (TSW) than Tongliao. Three-year average SY decreased with increased row spacings at both sites. Results suggest that in both climates, successful smooth bromegrass seed production was possible, but greater TSW is predicted for desert climates with good irrigation conditions than in semiarid continental monsoon climates due to greater sunshine duration (574 h compared with 527 h) and low relative humidity during seed development (48% vs. 66%). A seeding rate of .3 g m−1 and a row spacing of no wider than 30 cm appears to be adequate for smooth bromegrass seed production in these research locations and in similar ecological regions around the world.

Influence of salinity and temperature on the germination of Hedysarum scoparium Fisch. et Mey.

This study was conducted to determine the effects of temperature and salinity on seed germination and their recovery of germination after being transferred from saline conditions to distilled water. The germination responses of the seeds in complete darkness were determined over a wide range temperatures (10 to 35°C) and salinities (0 to 500 mM NaCl). Germination was inhibited above or below the optimal temperature of 15°C. The highest germination percentages were under non-saline conditions, and increased NaCl concentrations progressively inhibited seed germination. Germination rate decreased with increased salinity at all temperatures, but the highest rates were at 15°C. The interaction between salinity and temperature yielded no germination at 500 mM NaCl (25 and 35°C). After 10 days, seeds were transferred from salt solution to distilled water, and germination recovered at all temperatures with low salinity. At 500 mM NaCl, there was no germination recovery at 25 and 35°C. The results showed that salt stress decreased both the percentage and the rate of germination, exposure to high concentration of NaCl permanently inhibited germination at high temperature.